Coincident draft in relation to water demand is based on
- APeak hourly demand
- BMaximum daily demand
- CMaximum daily + fire demandCorrect
- DPeak hourly demand – fire demand
Solution
Concept
Coincident draft is the design draft when a fire occurs on the day of maximum demand.
Formula
Coincident draft = Maximum daily demand + Fire demand
Step-by-step solution
1. Fire can happen on any day, including the day of maximum demand. 2. Compare two cases: (a) maximum daily + fire demand, and (b) peak hourly demand. 3. The larger of the two is the design draft. 4. The case (a) is called the coincident draft.
Explanation
Coincident draft means the maximum daily demand plus the fire demand. It is compared with the peak hourly demand, and the larger value is used for design.
Why the other options are wrong
A is the peak hourly demand, which is a different case. B has no fire demand. D wrongly subtracts the fire demand.
Shortcut
Coincident = Max daily + Fire.
Common mistake
Forgetting to add the fire demand, or confusing it with peak hourly demand.
Correct answer: C) Maximum daily + fire demand